The present invention relates to a ruminal bolus for electronically identifying ruminants. The invention is particularly, but not exclusively, intended for use with ruminants living under agricultural conditions (cattle, buffalo, sheep, and goats), but is also applicable to industrial, hunting, or wild uses (reindeer, deer, and ruminants in general). The bolus can be used with animals of large weight (above about 25 kg), or of small weight (less than 25 kg), depending on the variant of the invention.
A conventional ruminal bolus is constituted by a body having an electronic device for storing and interchanging data, which device resides in one of the stomachs or pre-stomachs of a ruminant for tracking purposes. Its main use is identifying animals, monitoring production (weight gain, milk production, monitoring reproduction, state of health, . . . ) or for automating common operations concerning the management of such animals, such as feeding, or controlling access to restricted areas or controlling gates of classification runs, etc. In conventional manner, such information is delivered and picked up by means of electromagnetic waves.
Document U.S. Pat. No. 4,262,632 discloses an electronic identification system for herds of ruminants based on boluses, each comprising a transmitter which is administered orally as an alimentary bolus, and which is optimized to penetrate into the second pre-stomach referred to below as the xe2x80x9creticulumxe2x80x9d (honeycomb) of a ruminant. That device is in the form of a cylinder that is about 75 mm long, having a diameter of about 18 mm. To prevent any regurgitation phenomenon, it is recommended for the density of the device to exceed 2 g/cm3. To this end, provision is made to incorporate a weight inside the bolus, in the vicinity of the data interchange device.
Other types of known bolus can be received equally well in the reticulum or in the rumen (first pre-stomach).
By way of example, document WO 93-A-05 648 describes a bolus in the form of a cylinder or a flat capsule made of resin or of high density glass, and including an electronic device. That bolus is also provided with a continuous visible display system enabling the animal to be identified when the bolus is taken from a dead animal.
Document AU-A 64 92 12 describes an apparatus for identifying an animal based on a passive transducer included in a porcelain capsule and having a density of not less than 1.75 g/cm3. That system includes a magnetic block making it possible to take hold of the system after the animal has been slaughtered. The porcelain capsule is filled with a dense liquid in order to obtain the desired specific gravity for maintaining the transponder in an operational position.
In other types of bolus, an elongate body is used having one end ballasted with a mass of metal so as to confer the required density thereto and so as to ensure that the body remains implanted in a vertical position in the rumen or in the reticulum. One such bolus is described, for example, in document WO-A-95 17 809.
Although the presence of a mass of metal is advantageous in that it makes it possible to increase the density of the bolus, it nevertheless suffers from the following drawbacks. Firstly, it interferes with radio transmission between the electronic device within the bolus and the outside, in particular by shifting the frequencies of tuned circuits. Secondly, it frequently happens that the stomachs of ruminants contain, whether deliberately or involuntarily, foreign bodies or magnetized pieces which tend to collect around the metal piece, thereby attenuating transmission and reception signals, or causing the bolus to be rejected or expelled.
In most cases, it is observed that known boluses tend, either deliberately or accidentally, to take up final residence in the rumen. They therefore suffer from the drawback of being incapable of being used successfully until the suckler animal has developed a rumen. The range at which they can be read, and the effectiveness of such reading are also limited by the large size of the rumen and by the frequently random orientation of the electronic device in use.
An object of the invention is thus to provide a high density bolus enabling small dimensions to be used and as a result making it possible to fix the bolus reliably in the reticulum (second pre-stomach) of the ruminant, accurately located against the left costal wall, behind the heart.
Another object of the invention is to make it possible to mass-produce boluses at low cost.
A more general further object of the present invention is to make it possible to obtain a bolus that avoids the drawbacks of prior art boluses.
According to the invention, these objects are achieved by a bolus for electronically identifying a ruminant, the bolus being designed to be received in the reticulum of the ruminant and comprising a body, itself having a housing designed to contain a data interchange device (such as an electronic transponder), the bolus being characterized in that the body is made of a material based on alumina, Al2O3, and/or on silica, SiO2.
It has been discovered that alumina and silica provide two advantages, firstly they impart very high density to the body while presenting high resistance to the digestive juices and processes that take place in the pre-stomachs of ruminants. Secondly these materials are cheap and easy to use in mass-production methods.
In addition, these materials are non-magnetic and present excellent transparency at the radio-frequencies used for remotely interchanging data with the device housed in the body.
When the material is based on alumina, the content of the alumina present in the material is preferably not less than 60% by weight. Its content may lie in the range 75% to 99.5% by weight, and preferably lies in the range 80% to 99.5% by weight.
In a variant of the invention, silica represents the major portion by weight of the material. Under such circumstances, the silica can be present in the material at a content of not less than 40% by weight, preferably at a content of not less than 50% by weight, and more preferably, of not less than 55% by weight.
When silica is the majority material, alumina is preferably present in small quantities in the material, with the content of alumina preferably being less than 10% by weight, and more preferably less than 5% by weight.
In some variants of the invention, the alumina and the silica together constitute not less than 80% by weight of the composition of the material, and preferably not less than 90% by weight of the composition of the material.
To optimize the chemical composition of the material, it is possible to add thereto one or more of the following compounds: MgO, CaO, BaO, Na2O, K2O, Fe2O3, TiO2. Each of these compounds may be present at a content lying in the range 0.1% to 2% by weight.
When the bolus is made with a silica-based material, it is possible to provide for the compound MgO and for the silica together to constitute not less than 70% by weight, preferably 80% by weight, and more preferably still 85% by weight of the composition of the material. Under such circumstances, the MgO content may exceed 2%, and may even exceed 25% by weight.
Advantageously, the bolus does not include any added metal pieces (apart from the electronic circuit of the data interchange device) so as to benefit from the non-magnetic nature of the material used.
The composition of the material in the above-specified ranges makes it easy to achieve density of not less than 2.5 g/cm3. The density may be not less than 3 g/cm3, or indeed not less than 3.5 g/cm3.
Advantageously, the bolus is constituted by a symmetrical body with uniformly-distributed mass, such that its center of gravity and its geometrical center coincide.
In order to ensure that the bolus is properly fixed in the reticulum, the bolus is cylindrical in shape and circular in cross-section, with the edges of each of its ends being chamfered or rounded. This shape, in combination with an appropriate choice of dimensions, makes it possible in particular to fix the bolus in the direction of the major axis of the reticulum, in a position that is oblique and parallel to the diaphragm. This confers great stability and makes it possible to obtain optimum and uniform conditions for the electromagnetic link.
Such fixing can be obtained reliably when the ratio between the length and the radius of the bolus body lies in the preferred range of 2:1 to 5:1. Advantageously, this ratio lies in the range 2.5:1 to 4:1.
In a preferred embodiment for a bolus that is for use in ruminants of weight exceeding about 25 kg, and possibly reaching as much as 1,000 kg to 1,300 kg for bulls, the length of the body lies in the range 50 mm to 90 mm.
When the bolus is more particularly intended for use with ruminants of weight not exceeding about 25 kg, the length of the body preferably lies in the range 30 mm to 70 mm.
According to another characteristic of the bolus of the present invention, the housing for the electronic data interchange device comprises a cavity that is accessible from one end or from both opposite ends of the body. The cavity can be in the form of a blind hole on the main axis of the body or in the form of a through hole on the main axis of the body. Once the data interchange device has been put into place, the hole can be closed by means of an epoxy resin or a plastic cement that withstands the environment that obtains in the ruminant reticulum.
In a variant, the above-mentioned hole is closed at the or each end by means of a male part such as a pressure screw or a self-locking rivet suitable for fixing against the wall of the hole.
When the cavity is in the form of a through hole, it can be closed at each end by a self-locking rivet constituted by two separate elements, each having a portion of rod with a head at one end thereof, the two respective rods being disposed in such a manner as to engage via their free ends and to lock one within the other, clamping between them the data interchange device.
This disposition has the advantage of enabling the data interchange device to be installed prior to final assembly, and to ensure that it is accurately positioned automatically within the cavity. It also makes it possible to reduce the number of successive operations that need to be performed on the body of the bolus, since the device is put into place simultaneously with the rivet.
In a preferred embodiment of the invention, the bolus also includes a sleeve of resilient material designed to receive the data interchange device and having an outside diameter which enables it to fit without clearance inside the housing.
The present invention also provides a method of manufacturing a bolus of the kind described above, characterized in that it comprises the following steps: preparing a blend based on alumina, Al2O3, and/or based on silica, SiO2; forming a preform for the body of the bolus from the blend; and subjecting the preform to a firing step.
If necessary, the method further comprises a step of giving the bolus body preform its final dimensions and of finishing it after the firing step. The firing step may be performed at a temperature lying in the range 1000xc2x0 C. to 2500xc2x0 C. Nevertheless, it has been found that excellent results for the intended application are obtained when the firing temperature is substantially equal to 1400xc2x0 C.
In a preferred embodiment, the preform is made by extrusion and the extruded piece is cut to the general shape of the bolus body. Under such circumstances, the housing in the bolus body can be made by drilling prior to the firing step.
Nevertheless, it is also possible to make the bolus body by a molding method in which case the housing is formed simultaneously with the body.